Attention has recently been placed on display devices such as active matrix display devices using organic electroluminescent elements (hereinafter, referred to as “organic EL elements”) that are self-luminous and have wide viewing angles and quick responsiveness.
The display devices are configured by a display panel in which organic EL elements are disposed, and a drive circuit for driving the organic EL elements. The display panel is configured by disposing the organic EL elements in a matrix on a substrate such as glass, the organic EL elements including a first electrode such as aluminum (Al), a second electrode such as indium tin oxide (ITO) that opposes the first electrode, and a light emitting layer provided between the first electrode and the second electrode. The drive circuit is configured by, for example, thin-film transistors (TFTs) that are provided between the substrate and the first electrode and individually drive the organic EL elements.
The bottom emission method in which light emitted from the organic EL elements is extracted through the substrate to the outside, and the top emission method in which the light is extracted from the side of the second electrode that opposes the substrate are known as light emitting methods used in the display devices. Display devices using the bottom emission method have difficulty in ensuring a sufficient aperture ratio because of the presence of the thin-film transistors of the drive circuit on the substrate. On the other hand, the top emission method improves the efficiency of use of emitted light, as compared with the bottom emission method, because the aperture ratio is not restricted by factors such as the presence of the thin-film transistors.
The top emission method requires high optical permeability of the second electrode as well as high conductivity, because light is extracted through the second electrode formed on the upper surface of the light emitting layer to the outside. However, a transparent conductive material that is generally used for the second electrode is a metal oxide such as ITO or a metal thin film such as magnesium or aluminum, which has higher resistivity than metal layers used for wiring and other components. Thus, the larger is the display panel, the greater the difference in the wire length of the second electrode will be between light emitting pixels. This causes a large voltage drop between the edge of a power supply unit and the center of the panel and accordingly produces a difference in luminance and make the center of the panel dark. That is, there is a problem in that the unevenness in luminance depending on the positions of the organic EL elements arranged on the display panel surface causes unevenness in display.
To avoid this problem, it is effective to adopt a structure in which the second electrode provided in the upper part as a transparent electrode is connected to low-resistance wiring provided in the lower part. A display device disclosed in Patent Literature (PTL) 1 includes a first electrode that is provided separately from auxiliary wiring on a substrate, the first electrode and the auxiliary wiring being made of conductive materials having low resistivity, a light modulating layer that is provided on the first electrode and serves as a light emitting layer, and a second electrode that is made of a transparent conductive material and provided on the light modulating layer. The auxiliary wiring and the second electrode are connected to each other through openings formed in parts of a dividing wall.